Proteins & Amino Acids Chapter 6 Where do we get it? Animal foods – Also provide B vitamins and minerals such as iron, zinc and calcium Plant foods – Also provide B vitamins, iron, zinc, fiber and calcium, but in less absorbable forms Differences in fiber and fat content Protein’s Building Blocks: Amino Acids Variety in Amino Acid Structure Chemist’s View of Proteins More complex than carbohydrates or fats Twenty amino acids Different characteristics 9 essential amino acids The rest are either nonessential or conditionally essential Chemist’s View of Proteins Peptide bonds link amino acids Condensation reactions Multiple amino acids linked together: polypeptide Protein: one or more polypeptide chains Amino acid sequencing and protein structure Primary structure – chemical bonds Secondary structure – electrical attractions Tertiary structure – hydrophilic & hydrophobic Quaternary structure – two or more polypeptides Primary Structure: Amino Acid Sequence Secondary Structure: Alpha Helix and Beta Sheet Tertiary and Quaternary Structure Primary through quaternary structure Tertiary Structure Protein Shape and Function Denaturation Disruption of stability Uncoil and lose shape Occurs with exposure to acid or high heat Mutations: deviations in primary structure Mutations: Sickle Cell Anemia If structure is altered, shape and function may be affected Protein Digestion & Absorption Use of Amino Acids in Body Protein Synthesis Basis of uniqueness of each person DNA is the template Holds the code for amino acid sequences Structural proteins give us our shape Enzymes give us our metabolism Protein synthesis happens in every cell Diet can influence gene expression Sequencing errors can affect function DNA Transcription & Translation into Protein Sequencing Errors: Point Mutation Roles of Proteins Growth and maintenance Building blocks for most body structures Collagen Replacement of dead or damaged cells Enzymes Assist in break down, build up, and transform substances Catalysts: speed up chemical reactions B A A B New compound A B Enzyme The separate compounds, A and B, are attracted to the enzyme’s active site, making a reaction likely. Enzyme The enzyme forms a complex with A and B. Enzyme The enzyme is unchanged, but A and B have formed a new compound, AB. Stepped Art Fig. 6-9, p. 181 Roles of Proteins Hormones Messenger molecules Transported in blood to target tissues Regulators of fluid balance Hold fluid in the blood Without these proteins: edema Acid-base regulators Function as buffers Transporters – specificity Insulin: A Protein Hormone Protein Transporter: The Sodium-Potassium Pump Roles of Proteins Antibodies Defend body against disease Energy and glucose Alternative glucose source during starvation and insufficient carbohydrate intake Movement: contractile proteins in muscle Energy from Protein Protein Metabolism Protein turnover & amino acid pool Continual production and destruction Need dietary protein to maintain supply If needed for energy and glucose Wasting of lean body tissue Can lower BMR Extreme deprivation: organ proteins compromised Prevented by adequate intake of calories, carbohydrates, and fats Protein Metabolism Making proteins & nonessential amino acids If essential amino acid needed, body breaks down its own proteins Rate of protein synthesis may be compromised Limiting amino acid Nonessentials can be synthesized Making other compounds Neurotransmitters, hormones Melanin Nonessential Amino Acid Synthesis When a nonessential amino acid is not available from the diet, it can be made in the body by the process of transamination. Protein Metabolism Making fat Energy and protein exceed needs Carbohydrate intake is adequate Can contribute to weight gain Creates nitrogenous waste Nitrogenous waste In liver – ammonia converted to urea Filtered out of blood and excreted in urine by kidneys Nitrogenous Waste: Urea Protein intake and urea production Production increases in proportion to dietary protein Water consumption important in high protein diets Two factors Digestibility Protein Quality Animal proteins Plant proteins Amino acid composition Essential amino acid consumption Nitrogen-containing amino groups Limiting amino acid Health Effects of Protein High-protein diets Heart disease Increase risk correlated with high animalprotein intake Differences among protein selections Cancer Certain protein-rich foods, not protein content of diet, influence risk Individuals with kidney disease Acceleration of kidney deterioration Health Effects of Protein High-protein diets Osteoporosis Calcium excretion increases High animal protein intake more closely correlated with bone mineral loss Ideal amount has not been determined, and there are multiple influences on bone health Weight control Satiation and satiety Recommended Intakes of Protein Intake in U.S. and Canada typically adequate or more than adequate Dietary sources Serving sizes: what we get vs. what we need What is a standard serving size of meat? Key diet principle – moderation Leave room on the plate for other good stuff! Protein and Amino Acid Supplements Protein powders Muscle work vs. protein supplements Athletic performance Whey protein Impact on kidneys? Amino acid supplements Potential risks associated with intake Lysine & tryptophan